Antireflection film containing ultrafine particles, polarizing plate and liquid crystal display device

ABSTRACT

An antireflection film, containing ultrafine particles, formed of a resin composition having excellent dispersibility of ultrafine particles in a binder resin and capable of preventing whitening, a polarizing plate, and a liquid crystal display device are provided. 
     At least one resin layer is provided on a transparent substrate film directly or through other layer(s), and at least one of the resin layer has a controlled refractive index and is formed of a resin composition containing ultrafine particles. The outermost layer has a lower refractive index than an underlying layer in direct contact therewith. The resin composition contains a carboxyl-containing (meth)acrylate as part or the whole of a binder resin component. A polyfunctional acrylate having in its molecule three or more acryloyl groups may be added to the binder resin component in order to further enhance the properties of the hard coating.

FIELD OF THE INVENTION

The present invention relates to an antireflection film suitable forantireflection purposes in various displays of word processors,computers, and television, surfaces of polarizing plates used in liquidcrystal displays, optical lenses, such as sunglass lenses of transparentplastics, lenses of eyeglasses, finder lenses for cameras, covers forvarious instruments, and surfaces of window glasses of automobiles andelectric railcars, a polarizing plate, and a liquid crystal device.

BACKGROUND OF THE INVENTION

In the production of antireflection films, the provision of a layerhaving a specific refractive index, such as the formation of a layerhaving a lower refractive index than a transparent substrate film on thetransparent substrate film or the formation of a layer having a higherrefractive index than a transparent substrate film on the transparentsubstrate film followed by the formation of a layer having a lowerrefractive index than the transparent substrate film thereon, hashitherto been adopted in the art. Methods for controlling, that is,increasing or decreasing, the refractive index of the layer provided onthe substrate film include one wherein the refractive index is varied byvarying the kind of a binder resin used and one wherein ultrafineparticles having a refractive index different from a binder resin aredispersed in the binder resin.

In the conventional method wherein the refractive index is varied byvarying the kind of the binder resin, the control of the refractiveindex relies upon the selection of the resin, imposing a limitation. Onthe other hand, the method wherein ultrafine particles are dispersed inthe binder resin to control the refractive index has an advantage thatthe refractive index of the resin composition can be easily controlledas desired. Since, however, homogeneous dispersion of ultrafineparticles in the binder resin is so difficult that the use of such aresin composition disadvantageously results in, the formation of awhitened antireflection film, making it difficult to provide anantireflection film having excellent transparency and antireflectionproperties.

DISCLOSURE OF INVENTION

Accordingly, an object of the present invention is to provide anantireflection film using a resin composition which has excellentdispersibility of ultrafine particles in a binder resin and can preventwhitening, and another object of the present invention is to provide apolarizing plate and a liquid crystal display device using such anantireflection film.

In order to solve the above problems of the prior art, theantireflection film, containing ultrafine particles according to thepresent invention comprises: a transparent. substrate film; and at leastone resin layer provided on the transparent substrate film directly orthrough other layer(s), at least one of the resin layer(s) having acontrolled refractive index and formed of a resin composition containingultrafine particles, the outermost layer having a lower refractive indexthan the underlying layer in direct contact therewith, the resincomposition containing a carboxyl-containing (meth)acrylate as part orthe whole of a binder resin component.

The carboxyl-containing (meth)acrylate may be polyfunctional ormonofunctional. It is preferably one prepared by reacting a compoundhaving in its molecule one or more acid anhydrides with ahydroxyl-containing polyfunctional acrylate having in its molecule ahydroxyl group and three or more acryloyl groups because this reactioncan give an acrylic monomer having a high degree of oxidation by acarboxylic acid which can improve the dispersibility of ultrafineparticles in the binder resin and, at the same time, can impart hardproperties to a coating formed using this resin.

In addition to the carboxyl-containing (meth)acrylate, a polyfunctionalacrylate having in its molecule three or more acryloyl groups may beadded as one component of the binder resin, in which ultrafine particlesare to be incorporated, to the binder resin composition used in theantireflection film, containing ultrafine particles, according to thepresent invention, for the purpose of further enhancing the hardproperties. Another method for further enhancing the hard properties ofthe antireflection film containing ultrafine particles according to thepresent invention is to provide a layer, having hard properties,separately from the layer for controlling the refractive index.

In order to increase the refractive index of the coating, the aboveresin composition used in the antireflection film, containing ultrafineparticles, according to the present invention may contain at least onecompound selected from epoxy acrylates, aromatic compounds and halogencompounds other than F compounds.

The resin composition used in the antireflection film, containingultrafine particles, according to the present invention may optionallycontain an organic solvent. Further, the resin composition used in theantireflection film, containing ultrafine particles, according to thepresent invention may be used as an ionizing radiationcurable resincomposition. In particular, when it is used as an ultraviolet-curableresin composition, a photopolymerization initiator may be incorporatedinto the composition.

The polarizing plate of the present invention comprises a polarizingelement and, laminated thereon, the antireflection film containingultrafine particles according to the present invention.

The liquid crystal display device of the present invention comprises thepolarizing plate, of the present invention, as a component of the liquidcrystal display device.

One embodiment of the layer construction of the antireflection film,containing ultrafine particles according to the present invention issuch that a resin layer having a low refractive index formed of theabove resin composition containing ultrafine particles, the resin layerhaving a lower refractive index than the underlying layer in directcontact therewith, is formed on 2L transparent substrate film directlyor through other layer(s).

FIG. 1 shows one embodiment of the antireflection film, containingultrafine particles, according to the present invention. Thisantireflection film has the most fundamental layer construction. In FIG.1, numeral 11 designates a transparent substrate film, and a layer 13having a low refractive index is formed on the transparent substratefilm 11 to provide an antireflection film. In this antireflection film,the resin composition of the present invention can be used to form thelayer 13 having a low refractive index.

Another embodiment of the layer construction of the antireflection film,containing ultrafine particles according to the present invention issuch that a resin layer having a high refractive index formed of theabove resin composition containing ultrafine particles, the resin layerhaving a higher refractive index than the underlying layer in directcontact therewith, is formed on a transparent substrate film directly orthrough other layer(s) and, subsequently, a layer having a lowrefractive index, the refractive index of this layer being lower thanthe underlying layer in direct contact therewith, is formed on the layerhaving a high refractive index. Regarding the layer having a highrefractive index and the layer having a low refractive index, it is alsopossible to use a method wherein the layer having a high refractiveindex and the layer having a low refractive index constitutes one layerpair and at least one layer pair is formed on the transparent substratefilm. The above resin composition containing ultrafine particles may beused in any of the layer having a high refractive index and the layerhaving a low refractive index. Another embodiment of the layerconstruction of the antireflection film, containing ultrafine particles,according to the present invention is shown in FIG. 2. In FIG. 2, alayer 12, having a high refractive index, of which the refractive indexis higher than that of an adhesive layer 14, is formed on a transparentsubstrate film 11 through the adhesive layer 14, and a layer 13, havinga low refractive index, of which the refractive index is lower than thatof the layer 12 having a high refractive index, is formed on the layer12 having a high refractive index. The above resin compositioncontaining ultrafine particles may be used in any of the layer 12 havinga high refractive index and the layer 13 having a low refractive index.

A further embodiment of the layer construction of the antireflectionfilm, containing ultrafine particles, according to the present inventionis such that a layer, having a high refractive index, of which therefractive index is higher than that of the underlying layer in directcontact therewith, is formed on a transparent substrate film directly orthrough other layer(s) and the layer having a high refractive index isformed by using the above resin composition containing ultrafineparticles and comprises ultrafine particles bonded to one another with abinder resin. A layer having a low refractive index is then provided onthe layer having a high refractive index. One embodiment of theantireflection film having such a layer construction is shown in FIG. 3.In FIG. 3, a hard coat layer 15 having hard properties is formed on atransparent substrate film 11 through an adhesive layer 14, and anultrafine particle layer 22 having a high refractive index (a layer,having a high refractive index, comprising ultrafine particles mutuallybonded to one another with a binder resin), the refractive index of theultrafine particle layer being higher than that of the hard coat layer15, is formed on hard coat layer 15. Further, a layer 13, having a lowrefractive index, of which the refractive index is lower than that ofthe ultrafine particle layer 22 having a high refractive index is formedthereon. In the antireflection film shown in FIG. 3, the above resincomposition containing ultrafine particles may be used in any of thehard coat layer 15, the ultrafine particle layer 22 having a highrefractive index, and the layer 13 having a low refractive index.

In any of the exemplified antireflection films, the layer, having a lowrefractive index, as the surface layer may optionally have fineirregularities for antiglare purposes.

At least one of the layer(s), having a specific refractive index,provided on the transparent substrate film should be formed using theabove resin composition containing ultrafine particles from theviewpoint of the object of the present invention. However, there is noneed to form all of such resin layers using the resin compositioncontaining ultrafine particles in the present invention. For example,the highermost layer of the antireflection film may be an inorganiclayer, having a low refractive index, formed by vapor deposition, plasmaCVC and other processes conducted in vacuo.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing one embodiment, of theantireflection film containing ultrafine particles according to thepresent invention, having the most fundamental layer construction;

FIG. 2 is a cross-sectional view showing another embodiment of the layerconstruction of the antireflection film containing ultrafine particlesaccording to the present invention;

FIG. 3 is a cross-sectional view showing a further embodiment of thelayer construction of the antireflection film containing ultrafineparticles according to the present invention;

FIG. 4 is a cross-sectional view showing one embodiment of the layerconstruction of a polarizing plate with the antireflection film,containing ultrafine particles, according to the present invention beinglaminated thereto; and

FIG. 5 is a cross-sectional view showing one embodiment of the layerconstruction of a liquid crystal display using a polarizing plate withthe antireflection a film according to the present invention beinglaminated thereto.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will now be described in more detail.

Binder resin component

The binder resin component used in the resin layer for controlling therefractive index of the antireflection film, containing ultrafineparticles, according to the present invention should contain acarboxy-containing (meth)acrylate. Further, it may contain, in additionto the carboxy-containing (meth)acrylate, a polyfunctional acrylatehaving in its molecule three or more acryloyl groups or an epoxyacrylate.

(a) Carboxyl-containing (meth)acrylate

They "carboxyl-containing (meth)acrylate" of the binder resin componentused in a resin layer containing ultrafine particles in theantireflection film containing ultrafine particles according to thepresent invention can be prepared by reacting a compound having in itsmolecule one or more acid anhydride with a hydroxyl-containingpolyfunctional acrylate having in its molecule a hydroxyl group andthree or more acryloyl groups. The use of at least a carboxyl-containing(meth)acrylate as the binder resin can improve the dispersibility ofultrafine particles in the binder resin.

Specific examples of the "compound having in its molecule one or moreacid anhydride" include compounds having one acid anhydride group, suchas succinic anhydride, 1-dodecenylsuccinic anhydride, maleic anhydride,glutaric anhydride, itaconic anhydride, phthalic anhydride,hexahydrophthalic anhydride, methylhexahydrophthalic anhydride,tetramethylenemaleic anhydride, tetrahydrophthalic anhydride,methyltetrahydrophthalic anhydride, endomethylenetetrahydrophthalicanhydride, methylendomethylenetetrahydrophthalic anhydride,tetrachlorophthalic anhydride, tetrabromophthalic ; anhydride,chlorendic anhydride, and trimellitic anhydride; compounds having twoacid anhydride groups such as pyromellitic dianhydride,3,3',4,4'-benzophenonetetracarboxylic dianhydride, 4,4'-biphthalicanhydride, 4,4'-oxodiphthalic anhydride,4,4'-(hexafluoroisopropylidene)diphthalic anhydride,1,2,3,4-cyclopentanetetracarboxylic dianhydride,5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylicanhydride, 4-(2,5-dioxotetrahydrofuran-3-yl)-tetralin-1,2-dicarboxylicanhydride, 3,4,9,10-perylenetretracarboxylic dianhydride, and bicyclo 2.2. 2!octo-7-ene-2,3,5,6-tetracarboxylic dianhydride; and a mixture oftwo or more of the above compounds. When a compound having two acidanhydride groups among the above compounds is used, the resultantcarboxyl-containing polyfunctional acrylate has 3 to 10 acryloyl groupsand 2 to 3 carboxyl groups in the same molecule, which is particularlypreferred from the viewpoints of abrasion resistance and adhesion.

Specific examples of the "hydroxyl-containing polyfunctional acrylatehaving in its molecule a hydroxyl group and three or more acryloylgroups" include pentaerythritol triacrylate, dipentaerythritol.tetraacrylate, dipentaerythritol pentaacrylate, and a mixture of two ormore of them.

The reaction of the "compound having in its molecule one or more acidanhydride groups" with the "hydroxyl-containing polyfunctional acrylatein its molecule a hydroxyl group and three or more acryloyl groups" iscarried out by mixing "the hydroxyl-containing polyfunctional acrylatein its molecule a hydroxyl group and three or more acryloyl groups" and"the compound having in its molecule one or more acid anhydride groups"together in a molar ratio of not less than 1 and stirring the mixture at60° to 110° C. for 1 to 20 hr.

This reaction may be carried out in the presence of the "polyfunctionalacrylate having in its molecule three or more acryloyl groups" describedbelow and an organic solvent not containing any active hydrogendescribed below. The use of a polymerization inhibitor, for example,hydroquinone, hydroquinone monomethyl ether, catechol, p-t-butylcatechol, or phenothiazine, is preferred from the viewpoint ofpreventing polymerization derived from the acryloyl group during thereaction. The amount of the polymerization inhibitor used is 0.01 to 1%by weight, preferably 0.05 to 0.5% by weight, based on the reactionmixture.

For example, N,N-dimethylbenzylamine, triethylamine , tributylamine,triethylenediamine, benzyltrimethylammonium chloride,benzyltriethylammonium bromide, tetramethylammonium bromide,cetyltrimethylammonium bromide, zinc oxide and other catalysts may beused in order to accelerate the reaction. The amount of the catalystused is 0.01 to 5% by weight, preferably 0.05 to 2% by weight, based onthe reaction mixture.

The "carboxyl-containing (meth)acrylate" thus obtained can improve thedispersibility of the ultrafine particles and, when mixed with the"polyfunctional acrylate having in its molecule a hydroxyl group andthree or more acryloyl groups" described below, causes no lowering inacryloyl group density. Further, the adhesion to various plasticsubstrates can be improved, and a binder resin having excellent abrasionresistance is provided. This advantage is considered to be derived fromthe presence of a carboxyl group in the same molecule.

(b) Polyfunctional acrylate having in its molecule three or moreacryloyl groups

Specific examples of the "polyfunctional acrylate having in its moleculethree or more acryloyl groups" include trimethylolpropane triacrylate,EO-modified trimethylolpropane triacrylate, PO-modifiedtrimethylolpropane triacrylate, tris(acryloxyethyl) isocyanurate,caprolactone-modified tris(acryloxyethyl) isocyanurate, pentaerythritoltriacrylate, pentaerythritol tetraacrylate, dipentaerythritoltetraacrylate, dipentaerythritol pentaacrylate, dipentaerythritolhexaacrylate, alkyl-modified dipentaerythritol triacrylate,alkyl-modified dipentaerythritol tetraacrylate, alkyl-modifieddipentaerythritol pentaacrylate, caprolactone-modifieddipentaertythritol hexaacrylate, and a mixture of two or more. Amongthem, dipentaerythritol hexaacrylate, dipentaertythritol pentaacrylate,and a mixture thereof may be preferably incorporated into the component(a) when imparting hard properties to the coating is contemplated.

The weight ratio of the component (b) to the component (a) component(b)/component (a)! is not more than 2, preferably 0.01 to 2, morepreferably 0.1 to 2. When the weight ratio is less than 0.01, thestarting material for the component (a) is not easily available,rendering such a weight ratio unsuitable from the viewpoint of practicaluse. On the other hand, when it exceeds 2, the amount of the carboxylgroup becomes so small that the adhesion to various plastic substratesis unsatisfactory.

(c) Solvent

In the binder resin used in the present invention, a solvent isoptionally used in order to modify the viscosity of the resincomposition. Further, in the preparation of the "carboxyl-containing(meth)acrylate, " a solvent may be, if necessary, used. Solvents usableherein include aromatic hydrocarbons such as toluene and xylene; esterssuch as ethyl acetate, propyl acetate, and butyl acetate; alcohols suchas methyl alcohol, ethyl alcohol, n-propyl alcohol, iso-propyl alcohol,and n-butyl alcohol; ketones such as acetone, methyl ethyl ketone,methyl isobutyl ketone, and cyclohexanone; ethers such as2-methoxyethanol, 2-ethoxyethanol, 2-butoxyethanol, ethylene glycoldimethyl ether, ethylene glycol diethyl ether, and diethylene glycol.dimethyl ether; and ether esters such as 2-methoxyethyl acetate,2-ethoxyethyl acetate, and 2-butoxyethyl acetate. They may be used aloneor as a mixture of two or more.

Ultrafine particles

The ultrafine particles contained in the resin layer of theantireflection film, containing ultrafine particles, according to thepresent invention are divided into ultrafine particles having a higherrefractive index than the underlying layer in direct contact with theresin layer containing the ultrafine particles and ultrafine particleshaving a lower refractive index than the underlying layer in directcontact with the resin layer containing the ultrafine particles.

Examples of the ultrafine particles having a high refractive indexinclude ZnO (refractive index: 1.90), TiO₂ (refractive index: 2.3-2.7),CeO₂ (refractive index: 1.95), Sb₂ O₅ (refractive index: 1.71), SnO₂,ITO (refractive index: 1.95), Y₂ O₃ (refractive index: 1.87), La₂ O₃(refractive index: 1.95), ZrO₂ (refractive index: 2.05), Al₂ O₃(refractive index: 1.63), HfO₂ (refractive index: 2.00), and Ta₂ O₃.

Examples of the ultrafine particles having a low refractive indexinclude LiF (refractive index: 1.4), MgF₂ (refractive index: 1.4),3NaF·AlF₃ (refractive index: 1.4), AlF₃ (refractive index: 1.4), Na₃AlF₆ (cryolite, refractive index: 1.33), and SiO_(x) (x:1.50≦x≦2.00)(refractive index: 1.35-1.48).

The above ultrafine particles are used alone or as a mixture thereof,and the use thereof as a colloid prepared by dispersing the ultraf ineparticles in an organic solvent or water is advantageous from theviewpoint of dispersibility. The particle diameter is preferably notmore than 200 nm, more preferably 1 to 100 nm, particularly preferably 3to 20 nm because the ultrafine particles having such a particle diameteris not detrimental to the transparency of the coating. In the presentinvention, the mixing ratio of the binder resin to the ultraf ineparticles is such that the amount of the ultrafine particles is not morethan 10 parts by weight, preferably not more than 5 parts by weight,based on one part by weight of the binder resin. When the proportion ofthe ultrafine particles exceeds 10 parts by weight based on one part ofthe binder resin, the density of crosslinking with the acryloyl group inthe binder component is lowered, unfavorably resulting in deterioratedhard properties of the coating.

Light polymerization initiator and other components

When ultraviolet light is used as the ionizing radiation, the resincomposition used in the present invention comprises aphotopolymerization initiator in addition to the components (a) to (c).Photopolymerization initiators usable herein include benzoin methylether, benzoin ethyl ether, benzoin isopropyl ether, benzoin butylether, diethoxy acetophenone, benzyl dimethyl ketal,2-hydroxy-2-methylpropiophenone, 1-hydroxycyclohexyl phenyl 1 ketone,benzophenone, 2, 4, 6 -trimethylbenzoindiphenylphosphine oxide,2-methyl- 4-(methylthio)phenyl!-2-morpholino-1-propanone,2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butan-1-one, Michler'sketone, isoamyl N,N-dimethylaminobenzoate, 2-chlorothioxanthone, and2,4-diethylthioxanthone. These photopolymerization initiators may beused alone or optionally in combination of two or more. The amount ofthe photopolymerization initiator used is 0.1 to 10 parts by weight,preferably 1 to 5 parts by weight, based on 100 parts by weight in totalof the components (a) and (b).

Various additives, such as ultraviolet absorbers (for example,benzotriazole, benzophenone, salicylic acid, arid cyanoacrylateultraviolet absorbers), ultraviolet. stabilizers (for example, hinderedamine ultraviolet. stabilizers), antioxidants (for example, phenolic,sulfur, and phosphorus antioxidants), antiblocking agents, slip agents,and levelling agents, may be incorporated into the resin compositioncontaining ultrafine particles used in the present invention from theviewpoint of improving the coating properties.

Transparent substrate film

Films of triacetyl cellulose, diacetyl cellulose, acetate butylatecellulose, polyether sulfone, polyacrylic: resin, polyurethane resin,polyester, polycarbonate, polysulfone, polyether, trimethyl pentene,polyether ketone, (meth)acrylonitrile and the like are usable as thetransparent substrate film. Among them, a triacetyl cellulose film and auniaxially stretched polyester are particularly preferably used becauseit has excellent transparency and is not optically anisotropic. Ingeneral, the thickness of the film is preferably about 8 to 1000 μm.

Additional layer(s)

In the antireflection film, containing ultrafine particles, according tothe present invention, a layer(s) for imparting various functions,besides the above layers, may be additionally provided. For example, aprimer layer or an adhesive layer may be provided on the transparentsubstrate film from the viewpoint of improving the adhesion between thetransparent substrate film and the resin layer having a controlledrefractive index, and, further, a hard coat layer may be provided forimproving the hard properties. The refractive index of the additionallayer is preferably intermediate between the refractive index of thetransparent substrate film and the refractive index of the resin layerhaving a controlled refractive index.

The additional layer may be formed by direct coating on the transparentsubstrate film. Alternatively, when the resin layer having a controlledrefractive index is formed on the transparent substrate film by thetransfer process, the additional layer may be formed by a method whichcomprises forming an additional layer by coating on a resin layer,having a controlled refractive index, previously formed on a releasefilm, laminating a transparent substrate film onto the release film soas for the coating to face the transparent substrate film, and releasingthe release film from the laminate to transfer the additional layer tothe transparent substrate film.

Method for producing antireflection film containing ultrafine particles

One method for producing the antireflection film containing ultrafineparticles according to the present invention will be described. A resincomposition is coated on a transparent substrate film directly orthrough other layer(s). In this case, the resin composition has a lowerrefractive index than the underlying layer in direct contact with alayer to be formed by the resin composition and comprises ultrafineparticles, having a low refractive index, homogeneously dispersed in abinder resin part or the whole of which is constituted by acarboxyl-containing polyfunctional or monofunctional (meth)acrylate.Subsequently, the coating is dried to remove any solvent contained inthe coating and irradiated with an ionizing radiation by means of anionizing radiation irradiation apparatus, such as an electron beamirradiation apparatus or an ultraviolet light irradiation apparatus, tocure the coating, thereby preparing an antireflection film.

Another method for producing the antireflection film containingultrafine particles according to the present invention is as follows. Aresin composition is coated on a transparent substrate film directly orthrough other layer(s). In this case, the resin composition has a higherrefractive index than the underlying layer in direct contact with alayer to be formed by the resin composition and comprises ultrafineparticles, having a high refractive index, homogeneously dispersed in abinder resin part or the whole of which is constituted by acarboxyl-containing polyfunctional or monofunctional (meth)acrylate.Subsequently, the coating is dried to remove any solvent contained inthe coating and irradiated with an ionizing radiation by means of anionizing radiation irradiation apparatus to cure the coating. A layer,having a low refractive index, of which the refractive index is lowerthan that of the underlying layer in direct contact therewith, isprovided on the cured coating to prepare an antireflection film.

When a plurality of layers having a controlled refractive index areprovided, the highermost layer having a low refractive index may beformed by coating using a resin composition comprising ultrafineparticles, having a low refractive index, homogeneously dispersed in abinder resin part or the whole of which is constituted by a.carboxyl-containing polyfunctional or monofunctional. (meth)acrylate, oralternatively may be formed by subjecting ultrafine particles having alow refractive index to vapor deposition, CVD or other processesconducted in vacuo.

The resin composition containing ultrafine particles may be coated byvarious coating processes, such as slide coating, slot coating, curtainflow coating, and roll coating, or transfer process. In theantireflection film containing ultrafine particles according to thepresent invention, the surface of the highermost layer may have fineirregularities. Such irregularities can impart antiglare and/orantireflection properties to the antireflection film. The fineirregularities may be formed, for example, by laminating the necessarylayers on a release film having a finely irregular surface, laminatingthe resultant laminate on a transparent substrate film so as for thelaminated layer to face the transparent substrate film, and releasingthe release film from the laminate, thereby creating fine irregularitieson the surface of the laminate.

A pressure-sensitive adhesive may be coated on the underside of theantireflection film containing ultrafine particles according to thepresent invention so that the antireflection film can be applied to anobject for which antireflection is necessary, for example, polarizingelements.

In the antireflection film containing ultrafine particles according tothe present invention, the antireflection film has a lower reflectancethan the transparent substrate film.

Polarizing element and liquid crystal display

The antireflection film, containing ultrafine particles, according tothe present invention can be laminated onto a polarizing element toprovide a polarizing plate having improved antireflection properties. Apolyvinyl alcohol film, a polyvinyl formal film, a polyvinyl acetalfilm, and a saponified film of an ethylene-vinyl acetate copolymer,these films having been colored by iodine or a dye and stretched, may beused in the polarizing element. In the lamination of the antireflectionfilm, containing ultrafine particles, according to the presentinvention, to the polarizing plate, when the substrate film of theantireflection film, containing ultrafine particles, according to thepresent invention is, for example, a triacetyl cellulose film(abbreviated to "TAC film"), the TAC film is saponified in order toimprove the adhesion and for destaticization purposes. Thesaponification treatment may be carried out before or after theapplication of the hard coat on the TAC film.

FIG. 4 shows one embodiment of a polarizing plate using theantireflection film, containing ultrafine a particles, according to thepresent invention. In FIG. 4, numeral 4 designates one embodiment of theconstruction of the antireflection film, containing ultrafine particles,according to the present invention. The antireflection film 4 containingultrafine particles is formed by coating a resin composition comprisingultrafine particles, having a high refractive index, homogeneouslydispersed in a resin onto a TAC film 1 to form a layer 2 having a highrefractive index and further forming a layer 3 having a low refractiveindex on the layer 2 by using a resin composition comprising ultrafineparticles, having a low refractive index, homogeneously dispersed in aresin or alternatively by subjecting ultrafine particles having lowrefractive index to plasma CVD, vapor deposition or the like. Theantireflection film 4 containing ultrafine particles are laminated ontoa polarizing element 5, and a TAC film 1 is laminated on the other sideof the polarizing element 5. It is also possible to laminate theantireflection film 4, containing ultrafine particles, according to thepresent invention onto both sides of the polarizing element 5.

FIG. 5 is one embodiment of a liquid crystal device using theantireflection film containing ultrafine particles according to thepresent invention. In FIG. 5, the polarizing plate shown in FIG. 4, thatis, a polarizing plate having a layer construction of TACfilm/polarizing element/antireflection film containing ultrafineparticles, is laminated onto a liquid crystal display element 6, and apolarizing plate having a layer construction of TAC film/polarizingelement/TAC film is laminated onto the other side of the liquid crystaldisplay element 6. In the case of an STN type liquid crystal displaydevice, a phase difference plate is inserted into between the liquidcrystal display element 6 and the polarizing plate.

EXAMPLE 1

This example demonstrates an antireflection film wherein acarboxyl-containing (meth)acrylate containing ultrafine particles isused as a binder resin component of a layer having a low refractiveindex.

Preparation of carboxyl-containing (meth)acrylate:

163 parts of a dipentaerythritol hexaacrylate/dipentaerythritolpentaacrylate mixture having a dipentaertythritol pentaacrylate contentof 67% by mole (Kayarad DPHA, hydroxyl value 69 mg KOH/g, manufacturedby Nippon Kayaku Co., Ltd.) and 21.8 parts of pyromellitic dianhydride(dipentaerythritol pentaacrylate : pyromellitic acid dianhydride=2:1)were placed in a flask. 100 parts of methyl ethyl ketone, 0.1 part ofhydroquinone monomethyl ether, and 1 part of N,N-dimethylbenzylaminewere added thereto, and a reaction was allowed to proceed at 80° C. for8 hr. The resultant composition (1) had a solid content of 65.0%, acarboxyl-containing polyfunctional acrylate content of 44.3%, and adipentaerythritol hexaacrylate content of 20.4%.

Preparation of coating resin composition containing ultrafine particles:

The following materials were mixed together to prepare a resincomposition for a layer having a low refractive index.

    ______________________________________                                        Dispersion of ultrafine particles of SiOx                                                            36    parts by weight                                  (wherein 1 < × < 2) (manufactured by Nissan                             Chemical Industries Ltd.) in ethanol                                          Carboxy-containing (meth)acrylate                                                                    9     parts by weight                                  Solvent: toluene       7     parts by weight                                  ______________________________________                                    

Preparation of antireflection film containing ultrafine particles:

The resin composition, for a layer having a low refractive index,comprising the above components (37 wt % toluene solution) was coated ona polyethylene terephthalate film (thickness: 100 μm) to a thickness ofabout 90 nm on a dry basis, and the coating was irradiated with anelectron beam under conditions of 150 kv and 5 Mrad to cure the coating,thereby preparing an antireflection film.

EXAMPLE 2

This example demonstrates an antireflection film, containing ultrafineparticles, wherein both a layer having a low refractive index and alayer having a high refractive index contain a carboxyl-containing(meth)acrylate containing ultrafine particles.

A resin composition, for a layer having a high , refractive index,prepared by mixing 36 parts by weight of a dispersion of ultrafineparticles of ZnO in toluene (manufactured by Sumitomo Osaka Cemento Co.,Ltd.) with 9 parts by weight of the carboxyl-containing (meth)acrylateprepared in Example 1 was coated on a release film (trade name: MC-19,manufactured by REIKO CO., LTD.) to a thickness of 7 μm on a dry basis.The coating was irradiated with ultraviolet light at 320 mj and furtherirradiated with an electron beam under conditions of 175 kV and 7.5 Mradto cure the coating as a resin layer, thereby forming a layer having ahigh refractive index.

An adhesive comprising 6 parts by weight of Takelac A-310 (trade name,Takeda Chemical Industries, Ltd.), 1 part by weight of Takenate A-3(trade name, Takeda Chemical Industries, Ltd.), and 10 parts by weightof ethyl acetate was coated on the layer having a high refractive indexto a thickness of 3.5 μm, thereby forming an adhesive layer.

A TAC film (trade name: FT-UV-80, thickness 80 μm, Fuji Photo Film Co.,Ltd.) was laminated onto the layer having a high refractive indexthrough the adhesive layer, and the laminate was aged at 40° C. for 2 ormore days. The release film was then released from the laminate totransfer the layer having a high refractive index to the TAC film. Aresin composition, for a low refractive index, comprising 36 parts byweight of the dispersion of ultrafine particles of SiOx (wherein 1<×<2)(manufactured by Nissan Chemical Industries Ltd.) used in Example 1 and9 parts by weight of a carboxyl-containing (meth)acrylate (manufacturedby Mitsubishi Petrochemical Co., Ltd.) was coated on the surface of thelayer having a high refractive index remote from the TAC film to athickness of 100 nm on a dry basis to form a coating for a layer havinga low refractive index. The coating was irradiated with ultravioletlight at 640 mj to cure the coating, thereby preparing an antireflectionfilm, containing ultrafine particles, of Example 2.

EXAMPLE 3

This example demonstrates an antireflection film, containing ultrafineparticles, prepared using a carboxyl-containing (meth)acrylatecontaining ultrafine particles in a layer having a high refractiveindex.

A resin composition, for a layer having a high refractive index,prepared by mixing 36 parts by weight of a dispersion of ultrafineparticles of ZnO in toluene (manufactured by Sumitomo Osaka Cemento Co.,Ltd.) with 9 parts by weight of the carboxyl-containing (meth)acrylateprepared in Example 1 was coated on a polyethylene terephthalate releasefilm (trade name: Matt PET E-06, manufactured by Toray Industries, Inc.)having fine irregularities on its surface to a thickness of 7 μm on adry basis. The coating was irradiated with ultraviolet light at 320 mjand further irradiated with an electron beam under conditions of 175 kvand 7.5 Mrad to cure the coating as a resin layer, thereby forming alayer having a high refractive index.

An adhesive comprising 6 parts by weight of Takelac A-310 (trade name,Takeda Chemical Industries, Ltd.), 1 part by weight of Takenate A-3(trade name, Takeda Chemical Industries, Ltd.), and 10 parts by weightof ethyl acetate was coated on the layer having a high refractive indexto a thickness of 3.5 μm, thereby forming an adhesive layer.

A TAC film (trade name: FT-UV-80, thickness 80 μm, Fuji Photo Film Co.,Ltd.) was laminated onto the layer having a high refractive indexthrough the adhesive layer, and the laminate was aged at 40° C. for 2 ormore days. The release film was then released from the laminate totransfer the layer having a high refractive index to the TAC film. A 100nm-thick SiOx layer having a low refractive index was formed by plasmaCVD on the surface of the layer having a high refractive index remotefrom the TAC film to prepare an antireflection film, of Example 3,containing ultrafine particles and on its surface fine irregularities.

EXAMPLE 4

In this example, a carboxyl-containing (meth)acrylate was used in both aresin layer having a low refractive index and an ultrafine particlelayer having a high refractive index.

A resin composition, for a layer having a low refractive index,comprising 36 parts by weight of at dispersion of ultrafine particles ofSiOx (wherein 1<×<2) in ethanol (manufactured by Nissan ChemicalIndustries Ltd.) and 9 parts by weight of the carboxyl-containing(meth)acrylate described in Example 1 was coated on a release film(trade name: MC-19, manufactured by REIKO CO., LTD.) to a thickness of100 nm on a dry basis to form a coating for a layer having a lowrefractive index. The coating was irradiated with ultraviolet light at640 mj to cure the coating, thereby forming a layer having a lowrefractive index.

A resin composition, for a layer having a high refractive index,composed mainly of ultrafine particles, prepared by mixing 45 parts byweight of a dispersion of ultrafine particles of TiO₂ in toluene(manufactured by Sumitomo Osaka Cemento Co., Ltd.) with 1 part by weightof the carboxyl-containing (meth)acrylate used in Example L was coatedon the layer having a low refractive index to a thickness of 75 nm on adry basis. The coating was irradiated with an electron beam underconditions of 175 kV and 3 Mrad to half-cure the coating, therebyforming an ultrafine particle layer, having a high refractive index,with ultrafine particles mutually bonded through a binder resin.

A resin composition, for a hard coat layer, comprising 5 parts by weightof a polyester acrylate (trade name: EXD 40-9, Dainichiseika Color &Chemicals Manufacturing Co., Ltd.) and 10 parts by weight of isopropylalcohol was coated to a thickness of 5 μm on a dry basis. Thereafter,all the above resin layers were cured under conditions of acceleratingvoltage 175 kV and 10 Mrad to prepare a laminated film wherein a layerhaving a low refractive index, an ultrafine particle layer having a highrefractive index, and a hard coat layer were laminated in that order ona release film.

An adhesive comprising 6 parts by weight of Takelac A-310 (trade name,Takeda Chemical Industries, Ltd.), 1 part by weight of Takenate A-3(trade name, Takeda Chemical Industries, Ltd.), and 10 parts by weightof ethyl acetate was coated on the hard coat layer to a thickness of 3.5μm, thereby forming an adhesive layer.

A TAC film (trade name: FT-UV-80, thickness 80 μm, Fuji Photo Film Co.,Ltd.) was laminated onto the hard coat layer through the adhesive layer,and the laminate was aged at 40°C. for 2 or more days. The release filmwas then released from the laminate to transfer the hard coat layer(lowermost layer), the ultrafine particle layer having a high refractiveindex, and the layer having a low refractive index (uppermost layer) inthat order to the TAC film, thereby preparing an antireflection film,containing ultrafine particles, of Example 4.

EXAMPLE 5

This example demonstrates the use of a carboxyl-containing(meth)acrylate in an ultrafine particle layer having a high refractiveindex.

A resin composition, for a layer having a high refractive index,composed mainly of ultrafine particles, prepared by mixing 45 parts byweight of a dispersion of ultrafine particles of TiO₂ in toluene(manufactured by Sumitomo Osaka Cemento Co., Ltd.) with 1 part by weightof the carboxyl-containing (meth)acrylate used in Example 1 was coatedon a release film (trade name: MC-19, manufactured by REIKO CO., LTD.)to a thickness of 75 nm on a dry basis. The coating was irradiated withan electron beam under conditions of accelerating voltage 175 kV and 3Mrad to half-cure the coating, thereby forming an ultrafine particlelayer, having a high refractive index, with ultrafine particles mutuallybonded through a binder resin.

A resin composition, for a hard coat layer, comprising 5 parts by weightof a polyester acrylate (trade name: EXD 40-9, Dainichiseika Color &Chemicals Manufacturing Co., Ltd.) and 10 parts by weight of isopropylalcohol was coated to a thickness of 5 μm on a dry basis. Thereafter,all the above resin layers were cured under conditions of acceleratingvoltage 175 kV and 10 Mrad to prepare a laminated film wherein anultrafine particle layer having a high refractive index and a hard coatlayer were laminated in that order on a release film.

An adhesive comprising 6 parts by weight of Takelac A-310 (trade name,Takeda Chemical Industries, Ltd.), 1 part by weight of Takenate A-3(trade name, Takeda Chemical Industries, Ltd.), and 10 parts by weightof ethyl acetate was coated on the surface of hard coat layer of thelaminated film to a thickness of 3.5 μm, thereby forming an adhesivelayer.

A TAC film (trade name: FT-UV-80, thickness 80 μm, Fuji Photo Film Co.,Ltd.) was laminated onto the hard coat: layer through the adhesivelayer, and the laminate was aged at 40° C. for 2 or more days. Therelease film was then released from the laminate to transfer the hardcoat layer (lowermost layer) and the ultrafine particle layer having ahigh refractive index (uppermost layer) in that order to the TAC film,thereby preparing a laminated film. Further, a 100 nm-thick SiOx layerwas formed by plasma CVD on the ultrafine particle layer, having a highrefractive index, of the laminated film to prepare an antireflectionfilm, containing ultrafine particles, of Example 5.

EXAMPLE 6

A resin composition, for a layer having a high refractive index,prepared by mixing a mixture of 36 parts by weight of a dispersion ofultrafine particles of ZnO in toluene (manufactured by MitsubishiPetrochemical Co., Ltd.) with 2 parts by weight of the mixture describedin Example 1, that is, a dipentaerythritolhexaacrylate/dipentaerythritol pentaacrylate mixture having adipentaerythritol pentaacrylate content of 67% by mole (Kayarad DPHA,hydroxyl value 69 mg KOH/g, manufactured by Nippon Kayaku Co., Ltd.) and2 parts by weight of Aronix M-5300 (trade name) manufactured by ToaGosei Chemical Industry Co., Ltd. was coated on a release film (tradename: MC-19, manufactured by REIKO CO., LTD.) to a thickness of 7 nm ona dry basis. The coating was irradiated with an electron beam underconditions of 175 kV and 10 Mrad to cure the resin coating, therebyforming a layer having a high refractive index.

An adhesive comprising 6 parts by weight of Takelac A-310 (trade name,Takeda Chemical Industries, Ltd.), 1 part by weight of Takenate A-3(trade name, Takeda Chemical Industries, Ltd.), and 10 parts by weightof ethyl acetate was coated on the layer having a high refractive indexto a thickness of 3.5 μm, thereby forming an adhesive layer.

A TAC film (trade name: FT-UV-80, thickness 80 μm, Fuji Photo Film Co.,Ltd.) was laminated onto the layer having a high refractive indexthrough the adhesive layer, and the laminate was aged at 40° C. for 2 ormore days. The release film was then released from the laminate totransfer the layer having a high refractive index to the TAC film. A 100nm-thick SiOx layer having a low refractive index was formed by plasmaCVD on the surface of the layer having a high refractive index remotefrom the TAC film to prepare an antireflection film, of Example 6,containing ultrafine particles.

COMPARATIVE EXAMPLE 1

In this comparative example, an antireflection film not using anycarboxyl-containing (meth)acrylate in a binder resin composition wasprepared.

A 37 wt % solution of the following resin composition, for a layerhaving a low refractive index, in toluene was coated on a polyethyleneterephthalate film (thickness: 100 μm on a dry basis) to a thickness ofabout 90 nm, and the coating was irradiated with an electron beam underconditions of 150 kV and 5 Mrad to prepare an antireflection film.

Preparation of coating resin composition containing ultrafine particles:

    ______________________________________                                        Dispersion of ultrafine particles of SiOx                                                            36    parts by weight                                  (wherein 1 < × < 2) (manufactured by Nissan                             Chemical Industries Ltd.) in ethanol                                          Acrylic ester monomer (trade name: Kayarad                                                           9     parts by weight                                  TMPTA, manufactured by Nippon Kayaku Co.,                                     Ltd.)                                                                         Solvent: toluene       7     parts by weight                                  ______________________________________                                    

COMPARATIVE EXAMPLE 2

A resin composition, for a layer having a high refractive index,comprising 3 parts by weight of dihydroxyethyltetrabromobisphenolmethacrylate ester, not containing ultrafine particles having a highrefractive index, with a refractive index of 1.56 (trade name: NewFrontier BR-42, manufactured by Dai-Ichi Kogyo Seiyaku Co., Ltd.) and 6parts by weight of toluene was coated on a release film (trade name:MC-19, manufactured by REIKO CO., LTD.) to a thickness of 7 μm on a drybasis. The coating was irradiated with an electron beam under conditionsof accelerating voltage 175 kV and 10 Mrad to cure the coating, therebyforming a layer having a high refractive index.

An adhesive comprising 6 parts by weight of Takelac A-310 (trade name,Takeda Chemical Industries, Ltd.), 1 part by weight of Takenate A-3(trade name, Takeda Chemical Industries, Ltd.), and 10 parts by weightof ethyl acetate was coated on the layer, having a high refractiveindex, not containing ultrafine particles having a high refractive indexto a thickness of 3.5 μm on a dry basis, thereby forming an adhesivelayer.

A TAC film (trade name: FT-UV-80, thickness 80 μm, Fuji Photo Film Co.,Ltd.) was laminated onto the layer, having a high refractive index, notcontaining ultrafine particles through the adhesive layer, and thelaminate was aged at 40° C. for 2 or more days. The release film wasthen released from the laminate to transfer the layer having a highrefractive index to the TAC film, thereby preparing a laminated film.Further, a 100 nm-thick SiOx layer having a low refractive index wasformed as a layer having a low refractive index by plasma CVD on thelayer, having a high refractive index, of the laminated film, therebypreparing an antireflection film, of Comparative Example 2, notcontaining ultrafine particles.

COMPARATIVE EXAMPLE 3

A resin composition, for a high refractive index, comprising 3 parts byweight of the mixture described in Example 1, that is, a mixture of adipentaerythritol hexaacrylate/dipentaerythritol pentaacrylate mixturehaving a dipentaertythritol pentaacrylate content of 67% by mole(Kayarad DPHA, hydroxyl value 69 mg KOH/g, manufactured by Nippon KayakuCo., Ltd.), and 9 parts by weight of a mixed solvent of toluene : methylethyl ketone=1:1(that is, KT-11) was coated as a resin composition for alayer, not containing ultrafine particles, with a high refractive indexand having a hard property onto a release film (trade name: MC-19,manufactured by REIKO CO., LTD.) to a thickness of 7 pm on a dry basis.

The coating was irradiated with an electron beam under conditions ofaccelerating voltage 175 kV and 10 Mrad to cure the resin coating layer,thereby forming a layer, with a high refractive index, possessing a hardproperty.

An adhesive comprising 6 parts by weight of Takelac A-310 (trade name,Takeda Chemical Industries, Ltd.), 1 part by weight of Takenate A-3(trade name, Takeda Chemical Industries, Ltd.), and 10 parts by weightof ethyl acetate was coated on the layer having a high refractive indexto a thickness of 3.5 μm, thereby forming an adhesive layer.

A TAC film (trade name: FT-UV-80, thickness 80 μm, Fuji Photo Film Co.,Ltd.) was laminated onto the layer having a high refractive indexthrough the adhesive layer, and the laminate was aged at 40° C. for 2 ormore days. The release film was then released from the laminate totransfer the layer having a high refractive index onto the TAC film.Further, a 100 nm-thick SiOx layer was formed as a layer having a lowrefractive index by plasma CVD on the surface of the layer, having ahigh refractive index, remote from the TAC film, thereby preparing anantireflection film, of Comparative Example 3, containing ultrafineparticles.

Properties of the antireflection films prepared in Examples 1 to 6 andComparative Examples 1 to 3 were measured, and the results are given inTable 1.

(1) Haze

(2) Reflectance: Reflectance of an antireflection film at 550 nm with aspectrophotometer.

(3) Pencil hardness: Results of a test according to JIS K5400.

(4) Abrasion resistance: Difference in haze between before a Taberabrasion test and after the test; the abrasion resistance beingexpressed in terms of ΔH.

(5) Adhesion to substrate: The results of 5 consecutive tape peelingtests by the cross-cut adhesion method at the time of preparation of anantireflection film and after a wet heat test under 80° C. and 90% for1000 hr.

                  TABLE 1                                                         ______________________________________                                                             Adhesion                                                          Reflect-         Abrasion                                                                             Before After                                 Haze     ance    Pencil   resistance,                                                                          endurance                                                                            endurance                             (%)      (%)     hardness ΔH (%)                                                                         test   test                                  ______________________________________                                        Ex. 1 0.8    1.7     HB     6.6    100/100                                                                              100/100                             Ex. 2 0.8    1.5     H      5.7    100/100                                                                              100/100                             Ex. 3 23.3   1.0     2H     3.5    100/100                                                                              100/100                             Ex. 4 0.9    0.3     2H     5.0    100/100                                                                              100/100                             Ex. 5 0.8    0.3     2H     4.6    100/100                                                                              100/100                             Ex. 6 0.8    1.9     H      9.5    100/100                                                                              100/100                             Comp. 7.8    5.6     B      18.3    8/100  0/100                              Ex. 1                                                                         Comp. 0.9    2.4     5B     46.5    35/100                                                                               0/100                              Ex. 2                                                                         Comp. 1.0    3.6     2H     6.4    100/100                                                                              100/100                             Ex. 3                                                                         ______________________________________                                    

As is apparent from Table 1, the antireflection films prepared inExamples 1 to 6 have lower haze and reflectance, reduced whitening,i.e., better transparency, and better antireflection effect as comparedwith those prepared in Comparative Examples 1 to 3. Further, it isapparent that the antireflection films prepared in Examples 1 to 6 aresuperior to those prepared in Comparative Examples 1 to 3 in opticalproperties, such as antireflection, hard properties, such as pencilhardness and abrasion resistance, and adhesion between layers.

In the antireflection film containing ultrafine particles according tothe present invention, a resin composition wherein excellentdispersibility of ultrafine particles in a binder resin is used,offering low whitening, excellent transparency, and excellentantireflection effect.

The antireflection film containing ultrafine particles according to thepresent invention has, in addition to the above effects, excellent hardproperties and excellent adhesion between layers.

What is claimed is:
 1. An antireflection film comprising:a transparentsubstrate film; and at least one resin layer provided on saidtransparent substrate film directly or through (an)other layer(s), saidat least one resin layer having a controlled refractive index and formedof a resin composition containing ultrafine particles, the outermostlayer having a lower refractive index than the underlying layer indirect contact therewith and disposed on either the transparentsubstrate film or the transparent substrate film side, the resincomposition containing as at least part of a binder resin component acarboxyl-containing (meth)acrylate prepared by reacting a compoundhaving at least one acid anhydride in its molecule with anhydroxyl-containing polyfunctional acrylate having an hydroxyl group andat least three acryloyl groups in its molecule.
 2. The antireflectionfilm according to claim 1, wherein the resin composition contains apolyfunctional acrylate having in its molecule three or more acryloylgroups as part of the binder resin component.
 3. The antireflection filmaccording to claim 1, wherein the resin composition contains epoxyacrylate as part of the binder resin component.
 4. The antireflectionfilm according to claim 1, wherein the resin composition contains atleast one compound selected from aromatic compounds and halogencompounds other than F compounds.
 5. The antireflection film accordingto claim 1, wherein the resin composition is an ionizing radiationcuring resin composition.
 6. The antireflection film according to claim1, wherein the resin layer having a controlled refractive index has ahigher refractive index than the underlying layer in direct contacttherewith.
 7. The antireflection film according to claim 1, wherein theresin layer having a controlled refractive index has a lower refractiveindex than the underlying layer in direct contact therewith.